Hi Peter,
I tested the new Canson PhotoPro Matte canvas a few months ago, and had the same severe mottling problems you describe with both Timeless and Glamour II varnishes on all the small print samples I ran, both rolled and HVLP sprayed, and with both light and heavy coats. I showed the samples to Canson's technical expert, whose opinion was that the canvas simply needed more varnish (I had never had any such problems with my usual BC Lyve canvas).
Additional coats didn't seem to help much, and my remaining stock of varnish is vintage mid-2011 for the Timeless and early 2013 for the Glamour II, so at the time I put the problem down to either stale varnish (both had needed a lot of stirring to get an even mix), or an incompatibility with the Canson canvas. The latter is marked 'water resistant', so I surmised it might be somehow repelling the water-based varnish.
Not having any fresher supplies to hand, I very hesitantly sprayed a couple of A3 prints for a client on the ProPhoto Matte canvas a few weeks ago with the same batch of Timeless, assuming I might have to scrap them and start over with a new batch of varnish if necessary. To my surprise they came out perfectly and with no additional coats or effort required. I've also just done an A1+ on Canson's Museum Art canvas for another client, a very light coat of Timeless 80% matte in this case to meet a particular requirement, and again that came out perfectly with a single coat comprising one horizontal and one vertical pass, and no mottling or any other issues at all.
This was all with a Fuji Q4 HVLP system and undiluted Timeless sprayed at ca. 40 deg C. I did have to turn the air volume up slightly more than I normally use for diluted GII in order to get a fully atomised spray, but it's a lot easier and quicker on large prints than trying to roll coat.
BC may be correct that Timeless has a limited shelf-life (their latest spec. sheet now says six months, which I assume is a recent addition), and I'm afraid I don't have either an explanation for the original mottling problems or an answer for you, but my own experience suggests there may be more to this than simply an expired batch of varnish.
I hope you manage to find a solution in time for your show anyway.
Cheers,
Malcolm